Probing and Controlling the Bonds of an Artificial Molecule

Holleitner, Alexander W.; Blick, Robert H.; Hüttel, A. K.; Eberl, K.; Kotthaus, J. P.

doi:10.1126/science.1071215

Cited by 243 publications

(163 citation statements)

References 20 publications

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“…For the coupled DQD with degenerate energy levels, the Kondo behavior and the ISS interplay and strongly compete, as seen in the bulk two-impurity Kondo problem, [10] and a question arises whether there exists a spin entangled state composed of the coherent Kondo resonances. [11] Previous experimental and theoretical studies have mainly focused on the serial-coupled DQD [12,13,14,15,16,17,18,19], except for Ref. 9,19.…”

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confidence: 99%

Swapping Kondo resonances in coupled double quantum dots

et al. 2005

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Strong electron and spin correlations are studied in parallel-coupled double quantum dots with interdot spin superexchange J. In the Kondo regime with degenerate dot energy levels, a coherent transport occurs at zero temperature, where two entangled (bonding and antibonding) resonances are formed near the Fermi energy. When increasing J or the dot-lead parallel-coupling asymmetry ratio Γ2/Γ1, a swap between two entangled resonances occurs and the line shapes of the linear conductance are interchanged. The zero-bias differential conductance shows a peak at the critical values. Such a peculiar effect with the virtue of many-body coherence may be useful in future quantum computing.A large number of proposals have been made to materialize quantum bits (qubits) and quantum computing. Among these proposals, coupled quantum dot (QD) systems are particularly attractive.[1] The spin degree of freedom of the localized electrons on the dots is considered as a qubit due to the comparatively long coherence time. A key challenge is the construction of coupled double QD (DQD) to perform a swap operation, i.e. exchanging the electron spin states on the two dots. When the square root of a swap operation is combined with other isolated qubit rotations, a quantum controlled-NOT gate can be built and any quantum algorithms can be implemented.[2] In the coupled DQD, two local electrons form a singlet state. It has been proposed that the swap operation can be realized by tuning the time-dependent interdot spin superexchange (ISS) J(t) from positive to negative, flopping the singlet and triplet states. [1,3] In this Letter, we propose a simple and reliable mechanism to perform such a swap process in a parallel-coupled DQD at low temperatures. It has been well-established that under the Coulomb blockade with odd number electrons on a single QD, a quantum coherent many-body (Kondo) resonance is formed near the Fermi energy in the dot density of states (DOS) [4]. The Kondo effect for even number electrons on a single multilevel dot and possible phase transitions between singlet and triplet states have been considered for both "vertical" [5] and "lateral" [6,7,8,9] configurations. For the coupled DQD with degenerate energy levels, the Kondo behavior and the ISS interplay and strongly compete, as seen in the bulk two-impurity Kondo problem,[10] and a question arises whether there exists a spin entangled state composed of the coherent Kondo resonances.[11] Previous experimental and theoretical studies have mainly focused on the serial-coupled DQD [12,13,14,15,16,17,18,19], except for Ref. 9, 19. However, it has been recently realized that the serial geometry is unsuitable for studying this competition experimentally and a direct evidence for observing spin entanglement between the dot local electrons could be sought in the parallel coupled configuration. [20] It has thus motivated us to investigate whether and how this competition manifests itself in the coherent transport through DQD in the parallel configuration.For a degenerate DQD with ...

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Swapping Kondo resonances in coupled double quantum dots

et al. 2005

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“…Simultaneously, progress has been made in coupled quantum dot systems, where control of electron numbers in individual dots and coupling between the dots necessary to realise the building blocks for quantum information processing [11,12,13,14,15,16] has been demonstrated. Despite this progress many obstacles need to be overcome before elementary quantum operations on electron spinbased qubits [17,18,19,20] can be demonstrated.…”

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Voltage-controlled coded qubit based on electron spin

Hawrylak

Korkusiński

2005

Solid State Communications

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We design and analyze a solid state qubit based on electron spin and controlled by electrical means. The coded qubit is composed of a three-electron complex in three tunable gated quantum dots. The two logical states of a qubit, |0L and |1L , reside in a degenerate subspace of total spin S = 1/2 states. We demonstrate how applying voltages to specific gates changes the one-electron properties of the structure, and show how electron-electron interaction translates these changes into the manipulation of the two lowest energy states of the three-electron complex.

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“…In this paper, we analyze an electron Aharonov-Bohm (AB) interferometer consisting of two quantum dots (QDs) connected in parallel to two macroscopic leads such as have been demonstrated experimentally [4][5][6][7][8] . The role of quantum interference and Coulomb interactions in the conductance have been studied using both quantum rate equations (also known as master equations) [9][10][11][12] and Greens function technique [13][14][15][16] .…”

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Analysis of current and shot noise correlations in a double quantum dot interferometer with interdot spin interactions

et al. 2011

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We examine an electron Aharonov-Bohm (AB) interferometer with individual quantum dots connected in parallel to macroscopic leads. Here, we focus on the effect that both inter-dot spin-spin exchange interactions and intra-dot spin flips have on the current and frequency dependent current shot noise. By appropriate control of AB magnetic flux, inter-dot Coulomb repulsion, intra-dot spin flips, and inter-dot spin-spin coupling, the probability amplitudes for the different paths of the interferometer can be controlled leading to broad tunability of both the shape and contrast of interference fringes in the current. We also show that in the shot noise at finite frequencies corresponding to the spin-spin interaction energies the noise shows pronounced super-Poissonian and sub-Poissonian structure. AB flux, which is not an integer multiple of 2π, dramatically suppresses the correlations in the shot noise.

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Probing and Controlling the Bonds of an Artificial Molecule

Cited by 243 publications

References 20 publications

Swapping Kondo resonances in coupled double quantum dots

Swapping Kondo resonances in coupled double quantum dots

Voltage-controlled coded qubit based on electron spin

Analysis of current and shot noise correlations in a double quantum dot interferometer with interdot spin interactions

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